1. Field of the Invention
The present invention relates to an imaging apparatus, such as a digital camera, including a foreign substance removal mechanism to remove foreign substances adhering to the surface of an optical member.
2. Description of the Related Art
In recent years, an imaging apparatus, such as a digital camera, using an image sensor has been widely used. However, particularly, in a single-lens reflex type digital camera, a problem has arisen in which foreign substances may adhere to the surface of an optical member, such as an image sensor or a filter, thereby causing a captured image to contain an image of the foreign substances. The foreign substances are mostly dust, which enters from the outside to an imaging aperture when a lens is detached, and abrasion powder generated by operation of mechanical elements, such as a quick return mirror or a focal-plane shutter.
The foreign substance may be removed by spraying air on the surface of an optical member. However, it is difficult to completely remove the foreign substance. In such a case, work to wipe the surface of the optical member is required to remove the foreign substances. However, wiping the surface of the optical member by hand may cause surface irregularity or scratches on the surface of the optical member.
Accordingly, some apparatuses with simple mechanism have been proposed to remove foreign substances adhering to the surface of the optical member. A method of providing an optical member with vibration and dropping foreign substances adhering to the surface has been proposed and has actually been mounted on a camera. However, if the vibration is provided unnecessarily too much, it may cause such a failure that the vibrating optical member is broken. Thus, the amount of the vibration to be provided thereto has a limit. Accordingly, there has been a problem that a vibration type foreign substance removal apparatus cannot completely remove foreign substances having large adhesion.
Some other methods for removing foreign substances adhering to the surface of an optical member have been proposed. Japanese Patent Application Laid-Open No. 2005-292404 discusses a method for exposing the surface of an image sensor to the outside, allowing a foreign substance attracting member to enter the inside of a photographic optical path from the outside, and bringing the attracting member into contact with the surface of the image sensor with a suitable contact pressure to remove foreign substances.
In Japanese Patent Application Laid-Open No. 2001-298640, a method is discussed in which a wiper member is incorporated in a camera. The wiper member is brought into contact with the surface of an image sensor and scans thereon by motor drive.
In Japanese Patent Application Laid-Open No. 2006-119461, a method is discussed in which an electrically charged member scans the surface of an image sensor, without contact therewith, to remove foreign substances therefrom using electrostatic force.
An apparatus discussed in Japanese Patent Application Laid-Open No. 2005-292404 is an accessory apparatus which is attachable to an outside of a camera to be operated by a user. When cleaning is required, a lens must be removed and the accessory apparatus must be attached, so that the operation is intricate. Accordingly, there may be a problem for a user to miss a photo opportunity.
In an apparatus discussed in Japanese Patent Application Laid-Open No. 2001-298640, a wiper member or the like is incorporated inside a camera, so that foreign substance removal operation can be simply performed at any timing. However, since the wiper member is disposed between a shutter blade and an image sensor, this may cause restrictions on the arrangement of elements. In particular, the traveling surface of the shutter blade is away from an imaging surface, thus reducing shutter efficiency. Accordingly, there has been a problem that moving body stop capability is inferior at a high shutter speed.
Further, when shutter efficiency needs to be kept as high as possible, it is necessary for a wiper member to be thinned. Accordingly, there has been a problem that the wiper member is inferior in strength and location accuracy. In particular, when the wiper member is limited to a thin material, a spring constant is increased even if it is an elastic body. Therefore, it is difficult for the wiper member to give a constant pressure on the surface of an image sensor. The pressure significantly varies due to a slight accuracy error of the wiper member. Thus, this may result in such a state that foreign substances cannot be removed or it may cause scratches on the surface of the image sensor.
An apparatus discussed in Japanese Patent Application Laid-Open No. 2006-119461 uses an electric charge unit also as a shutter blade, so that restrictions on the arrangement of elements and deterioration in shutter efficiency can be reduced to be minimum. However, an increase in inertia moment of the shutter blade causes problems that a high shutter speed cannot be achieved and the shutter blade is inferior in durability. Further, when an electric charge member is separately provided and scans between the shutter device and the image sensor, similar to the apparatus discussed in Japanese Patent Application Laid-Open No. 2001-298640, this causes restrictions on the arrangement of elements. In addition, the shutter blade traveling surface is away from the imaging surface, so that the shutter efficiency is decreased and the moving body stopping capability is inferior at a high shutter speed.